Beryllium window x-ray tube



1958 J. J. c. HARDENBERG 2,866,114

BERYLLIUM WINDOW X-RAY TUBE Filed June 15. 1954 I. I'll. 'IIIIIII'I "I".'11-'11. 'IIIIIIII VIIIIIIIIIII'IIIIIIIIIIIIIII w sm I ......m.............................n..

INVENTOR A Jn Jsayas, C/W/Lsf/aa/Y Harde/ze y AGENT United States Patenti 2,866,114 BERYLLIUNI WINDOW X-RAY TUBE Jan .l'esayas ChrisfiaanHardenberg, Eindhoven, Netherlands, assignor, by mesne assignments, toNorth American Philips Company, Inc., New York, N. Y., a corporation ofDelaware Application June 15, 1954, Serial No. 436,922 Claims priority,application Netherlands June 12, 1953 4 Claims. (Cl. 313-59) Thisinvention relates to devices containing radiationtransparent windows,and in particular to X-ray tubes containing a beryllium window.

It is known to use X-rays in a manner such that the long-wave part ofthe X-ray spectrum is utilised. A suitable choice of the voltage betweenthe anode and the cathode of the X-ray tube ensures the major portion ofthe ray output to have the required wavelength. However, if therequirement is to be satisfied that the wavelength exceeds 4 A., inwhich case the applied voltage is approximately 5 kv. in order to obtaina maximum ray output, difficulties arise. X-rays having such awavelength are highly attenuated when they penetrate the very thin layerof material which forms the partition between the evacuated space in thetube and the environment and the effect of this detrimental phenomenonincreases with increase in the wavelength. Consequently the need forever thinner windows made of a material absorbing a minimum amount ofrays arises. The most suitable material is beryllium. A-n X-ray tube hasalready been manufactured comprising a window of this material 200,11.thick. The tube had to be connected permanently to the vacuum pump sincethe beryllium plate arranged in the ray window did not form a completelyairtight seal.

This circumstance interferes with the development of the art ofphotographic registration of tissue structures by means of X-rays. Itwas found that the examination of such objects includes a region inwhich the resolving power of the light microscope is not sufficient. Thefineness of the tissue structure requires a resolving power preferablyexceeding 1 micron which can be approximated to by a contactregistration by means of X-rays. Registrations of tissue layers 30 1.thick have already been made.

The invention relates to an X-ray tube comprising aradiation-transparent metal window of slight thickness in order to sealthe radiation aperture in an airtight manner, which window is made ofberyllium. According to the invention the beryllium window is less than100 microns thick for part of its surface area. Technical difficultiesapparently did not allow the manufacture of windows passing X-rays of awavelength exceeding 4 A. in a sufficient degree. These difiicultieshave been overrated and according to the invention it was found that avery careful treatment allowed the manufacture of windows which were100p. thick or even thinner while starting from known methods. Ifsufficient care is taken the desired result is obtained in that thewindow is rubbed along a flat surface with the use of a small amount ofvery fine grinding powder. Thus the resultant window of beryllium has aground portion less than 100 microns thick that is air-tight orvacuum-tight.

In most cases a radiation field of small size is sufficient to make aregistration since this can be enlarged several times optically forexamination. If only that part of the window which passes the usefulrays has to creases the resistance of the window to the atmosphericpressure.

From a calculation of the X-ray absorption it was found that in the caseof an absorption in the tissue layer of from 20 to the lowest absorptionlimit indicating the difference in intensity which can just be observed,the wavelength is 4 to 8 A, with a 20 1 tissue. With 10y. tissue thisvalue is 5 to 10 A. and with 5 tissue the wavelength would have to be 6to 12 A. The invention permits the examination to be extended to coverthese tissue layers since the ray window sufficiently passes therequired wavelength spectrum.

The drawing shows an embodiment of an X-ray tube according to theinvention.

The X-ray tube is connected to the end of a high tension supply cable 1.A current supply conductor 2 of the cable 1 is secured to the anode hood3 of the X-ray tube. The anode hood 3 together with a glass cylinder 4to which it is sealed anda cylindrical metal part 5 sealed to the otherend of the glass cylinder 4 forms the wall of the X-ray tube envelope.The tube is surrounded by a metal sheath 6 which forms an integralstructure with the earthed cable sheath 7. The anode 8 is secured to theanode hood 3. It extends close to a window 9 secured to the cylindricalpart 5. The window hermetically seals the cylinder aperture. The vacuumspace within the tube wall also contains a focusing member 10 and athermionic cathode 11. The cathode is held by a current supply wire 12and a cathode support 13. Electrons emitted from the cathode 11 strikethe end face 15 of the anode 8 and are focused thereon into a smallfocal point by means of the focusing member 10. The X-rays penetrate thewindow 9 in the direction of the tube axis.

The window 9 is made of ground beryllium foil the thickness of which isso slight that soft X-rays are absorbed to a small extent. The window isless than 0.1 mm. thick and the X-ray tube produces a radiation of suchslight hardness that a field of examination which is highly important tomedical science can be considerably extended.

What is claimed is:

1. A discharge device comprising an envelope containing an atmospheredifferent from the outside atmosphere, cathode and anode electrodes, anda radiationtransparent window in said envelope, said window comprisingvacuum-tight beryllium foil having a ground portion of a thickness lessthan microns.

2. An electron discharge device comprising an evacuated envelope,cathode and anode electrodes, and a radiation-transparent window in saidenvelope, said window comprising vacuum-tight beryllium foil having aground portion of a thickness less than 100 microns.

3. A device as set forth in claim 2 wherein thelessthan-lOO-microns-thick foil portion is surrounded by a berylliumportion of greater thickness for strengthening purposes.

4. An X-ray tube comprising an evacuated envelope, cathode and anodeelectrodes, and an X-radiation-transparent window in said envelope andcapable of transmitting X-rays of a wavelength exceeding 4 Angstroms,said window comprising vacuum-tight beryllium foil having a groundportion of a thickness less than 100 microns.

References Cited in the file of this patent UNITED STATES PATENTS1,942,007 Slack Ian. 2, 1934 2,332,426 Atlee Oct. 19, 1943 2,394,984Claussen Feb. 19, 1946 2,440,348 Root Apr. 27, 1948 2,665,391 BleeksmaJan. 5, 1954

1. A DISCHARGE DEVICE COMPRISING AN ENVELOPE CONTAINING AN ATMOSPHEREDIFFERENT FROM THE OUTSIDE ATMOSPHERE, CATHODE AND ANODE ELECTRODES, ANDA RADIATIONTRANSPARENT WINDOW IN SAID ENVELOPE, SAID WINDOW COMPRISINGVACUUM-TIGHT BERYLLIUM FOIL HAVING A GROUND PORTION OF A THICKNESS LESSTHAN 100 MICRONS.